Field of the Invention
The invention relates to a pressure reservoir for a fuel supply system. The pressure reservoir is formed of an elongated hollow body with an inlet connection for communicating with a high-pressure pump and at least two outlet connections for communicating with injection valves.
Such pressure reservoirs are used above all in injection systems known by the name "common rail", which makes it possible to keep the injection pressure and the injection quantity independent of the engine speed, and moreover to increase the injection pressure to above 1500 bar. In the common rail injection systems, fuel is pumped by a high-pressure pump out of a tank into the pressure reservoir, by way of which the fuel is present at injection valves that are each disposed in the cylinder heads of an engine. The pressure reservoir is generally tubular in shape and oriented parallel to the cylinder heads. The outlet connections for the injection valves disposed in the cylinder heads are generally disposed along the tubular body in a spacing equivalent to the spacings between individual injection valves.
The injection events into the cylinders are tripped by supplying current to the appropriate injection valves. The injection volume depends on the pressure prevailing at the injection valves and on the duration of the supply of electrical current. The injection events performed by the injection valves cause pressure fluctuations in the pressure reservoir. However, because of the position of the outlet connections that are distributed over the length of the tubular body, a variable effect on the individual injection valves and on the injection events performed by these injection valves can occur, and in particular can lead to variations in the respective injection volume.
To prevent such disadvantageous pressure fluctuations in the pressure reservoir that are tripped by the injection events, it is known from Published, Non-Prosecuted German Patent Application DE 195 32 599 A1 to divide the pressure reservoir into two individual reservoirs. In the application, each reservoir communicates with the common high-pressure pump via a respective distributor element. The individual reservoirs are then loaded in accordance with the ignition sequence of the engine, thus assuring that for the successive injection events, an unloaded individual reservoir will be available, and thus the pressure fluctuations tripped by one injection event cannot affect the next injection event. However, the embodiment involves increased production and installation expense, because both two pressure reservoirs and an additional distributor element have to be manufactured and installed in the engine compartment.
Furthermore, as in the conventional tubular pressure reservoirs, the outlet connections assigned to the various injection valves in the individual reservoirs used in Published, Non-Prosecuted German Patent Application DE 195 32 599 A1 are disposed along the tubular body. However, since in the region of the outlet connections the material load resulting from the internal pressure in the pressure reservoir is multiplied, the wall thickness and material strength in the region of the outlet connections must be oversized considerably compared with the other regions. This leads to both a high weight of the pressure reservoir and high costs for materials. Moreover, autofrettage is as a rule necessary as well.